1. Field of the Invention
The present invention relates to an ink recycling type inkjet printer that performs printing by discharging a recycled ink from an ink head, and more particularly, to a technology for shortening the time required to make a temperature of a recycled ink reach a predetermined temperature by varying the ink recycling amount.
2. Description of the Related Art
It is known that an inkjet printer performs printing on a recording medium, such as printing paper, by discharging ink from a nozzle of an ink head. Further, as the inkjet printer, there is an ink recycling type inkjet printer that continuously recycles ink at the time of a printing state so as to cool ink or remove wastes in an ink channel.
The ink recycling type inkjet printer includes an ink recycling path to recycle ink, wherein a downstream side and an upstream side of the ink recycling path are installed with ink tanks through the ink head. Further, a pump, which applies pressure so as to recycle the ink, is installed between the ink tanks.
Further, the ink recycling type inkjet printer is installed with a temperature sensor that detects at all times whether or not a temperature of ink (recycled ink) being recycled through the ink recycling path at the time of a printing state is a temperature (predetermined temperature) suitable for printing. At this time, if the temperature of the recycling ink is lower than the predetermined temperature, viscosity of ink is increased, such that when a discharge of the ink is poor. To the contrary, if the temperature of the recycling ink is higher than the predetermined temperature, viscosity of the ink is decreased, such that an amount of ink discharged from the nozzle is increased, causing the printing quality to change.
For these reasons above, in the case where the inkjet printer is not used for a long time, etc., when the temperature of ink is at a low temperature, there is a need to increase (warm up) the temperature of the recycled ink using a heating unit, which is installed in the ink recycling path, while recycling the ink for a predetermined time so as to generate optimal printing. Further, for continuous printing over a long period of time, when the recycling ink is at a high temperature, the temperature of the recycling ink should be reduced by a cooling unit that is installed in the ink recycling path.
Moreover, the ink head can be cooled by making the ink head be configured with an ink recycling structure, such that the ink head is used for the ink recycling type inkjet printer.
For example, an ink head of the ink recycling structure as disclosed in JP-A-2006-88575 is installed with plural individual channels, which are partitioned by plural partition walls configured of a piezoelectric element and are installed between an ink supplying hole and an ink discharging hole inside of the ink head. As a result, the ink supplied from the ink supply hole flows in the individual channels so that most of the ink can be discharged from the nozzles that are installed in the individual channels. However, ink, which is not discharged, is discharged from the ink discharging hole and-then recycles through the ink recycling path as described above and re-supplied to the ink head. With the ink head as described above, since the ink head heated due to continuous printing over a long period of time is cooled by the recycling ink within the ink head, continuous printing time can be extended.
However, in order for the ink recycling type inkjet printer described above to increase the temperature of the recycling ink up to the predetermined temperature at the time of warming up and the like, there is a problem in that more time is required to warm up the ink recycling type inkjet printer as the ink recycling amount is increased. For example, when the ink recycling amount is 1.0 [L], the specific heat of the recycling ink is 3.0 [J/g*K] and the density of the recycling ink is 1.0 [g/cm3], thus, the heat capacity of the recycling ink becomes 3,000 [J/K] and even if a heater having 200 W output is used, it takes 5 to 6 minutes to increase the temperature of the recycling ink to 5° C. Further, if the output of the heater is increased so as to shorten the time required to increase the temperature, a large amount of power is consumed.
Furthermore, even though the temperature increase of the ink head is suppressed by using the ink head configured as the ink recycling structure as disclosed in JP-A-2006-88575, since the ink is subjected to an increase in temperature due to the heat generated from the ink head recycling the ink through the ink recycling path, the temperature of the recycled ink is still increased. Also, in order to reduce the temperature of the recycling ink up to the predetermined temperature, time is needed, similar to the case of increasing the temperature.